Paper sizing lubricant composition comprising a fatty acid and non ionic lubricant



United States Patent 3,357,844 PAPER SIZING LUBRICANT COMPOSITION COMPRISING A FATTY ACID AND NON IONIC LUBRICANT Robert L. Wood and Charles Galusha, West Linn, Greg, and Herman F. Mader, Lakewood, Calif., assignors, by direct and mesne assignments, to Crown-Zellerbach Corporation, San Francisco, Calif., a corporation of Nevada No Drawing. Filed Oct. 23, 1964, Ser. No. 406,172 6 Claims. (Cl. 106-159) This invention relates to the art of coating paper and the like, and more particularly concerns a coating composition, and method and means for its preparation, having incorporated therein an oleaginous substance facilitating the preparation of smooth coatings with proper lubricity.

By way of introduction, in the coating of paper to pre pare, for example, a publication grade paper, a coating may be applied to one or both faces of the web which comprises a mineral pigment (such as clay, chalk, titanium oxide, etc), an adhesieve or binder (such as protein, cooked starch, and casein), and water which forms a suspension of pigment. In the past it has been proposed to add lubricating materials to such compositions whereby their flowability is improved and to eliminate such problems as dusting which occurs after a coating is spread on a web. To further explain this latter point, in making a glossy coated paper, the paper after being supplied with coating may be passed through the bite defined by two calender rolls rotated at similar speeds and forced at high pressure against opposite faces of the paper. The action of the rolls tends to break down the coating, and in the absence of slipperiness in the coating, the material forming the coating disintegrates to produce the above referred to dusting.

A number of materials have been suggested for giving lubricity to coatings including such substances as calcium and ammonium stearate. Use of these materials has introduced certain diificulties, however. Calcium stearate is insoluble in water and difficult to disperse in an aqueous suspension. As a consequence, special procedures have had to be adopted to produce a proper mixture of the stearate. Relatively large amounts of calcium stearate are needed to obtain the lubricious properties desired, and thus its use has entailed some expense. Ammonium stearate is soluble in water, however, it tends to thicken coatings excessively, which has prevented wide use of the material with blade-type coaters. The relatively high viscosity of coatings including ammonium stearate also tends to set a limit on the solids content that may be incorporated in the coatings. A high solids content in a coating has some definite advantages (for instance, such coatings are more easily dried than coatings containing more water), and thus this has been a further disadvantage in using ammonium stearate.

A general object of this invention is to provide improved coating compositions, which feature fatty acids derived from animal or vegetable oils and fats as an oleaginous substance imparting flowability and lubricity to the compositions, and a dispersant for such acids operable to prevent their separation in the aqueous suspension which normally forms the usual coating composition. It has been discovered that according to this invention, and upon utilizing such fatty acids together with suitable dispersants, the desired properties are obtained in a coating, and quite surprisingly, these properties result with the use of substantially less material than when such substances as calcium or ammonium stearate are employed. Further,when a fatty acid and dispersant are present, many ICC of the difiiculties attending the use of conventional materials are eliminated.

Another object of the invention is to provide an improved process for preparing coating compositions, including such fatty acids whereby good dispersion of the fatty acids in the compositions is produced.

Yet a further object is to provide an additive for coating compositions, containing a fatty acid and a dispersant, which facilitates the manufacture of a coating composition with desired lubricity.

Various other objects and advantages of the invention will become more fully apparent from reading of the following description, which includes certain specific examples included primarily for purposes of illustration.

As indicated above, coating compositions such as may be used in manufacturing coated paper may comprise an aqueous suspension of a mineral pigment or filler, having mixed therewith an adhesive or binder slurry comprising cooked starch, protein, or casein suspended in water. Typically a paper coating composition may be prepared using a pigment suspension and starch slurry or solution prepared as follows (parts and percentages herein are on a weight basis).

Pigment suspension An aqueous suspension of pigment is prepared by mixing 100 parts Georgian coating clay and 43 parts water, to obtain an aqueous mixture containing 70% solids. Added to this mixture is .3 part T.S.P.P. (tetrasodiumpyrophosphate) as a dispersant for the clay. The resulting suspension is the consistency of cream and a viscosity (Brookfield) of 250 centipoises at 20 r.p.m. (70 F.).

Starch solution A cooked starch solution containing 30% starch is prepared by mixing 15 parts starch and 35 parts water to obtain a slurry. A small amount of enzyme (the proportion used being /2 pound enzyme per 5000 pounds of starch) is then added to the slurry, and the mixture cooked at about 170 F. for 10 minutes, to break down the starch. The solution is then raised to 210 F. and held at this temperature for about 20 minutes to kill the enzyme, with the production of a final starch solution having a viscosity (Brookfield) of centipoises at 20 rpm. (tested at 205 F.).

According to this invention, such a clay suspension and starch solution is mixed to form a coating composition, and there is stirred in with the mixture preparatory to making the final composition an additive mixture comprising a fatty acid (this term including mixtures of specific fatty acids) derived from animal or vegetable oils and fats, including unsaturated oils and fats which have been hydrogenated, and a nonionic dispersant. Stated otherwise, the acid employed comprises fatty acids having chain lengths of from 14 to 22 carbon atoms (thus referred to as long chain fatty acids), which are predominately saturated to provide a solid in the coating. Preferably, the fatty acid is blended with the nonionic surfactant or dispersant before its addition to the coating composition, and the two materials introduced simultaneously to the starch solution while the latter is still hot, as in this way the fatty acid is readily incorporated into the starch with a complete and thorough dispersion of the fatty acid, which dispersion remains throughout the entire coating process.

The following formulations are exemplary of fatty acid mixtures of the type that may be incorporated directly with a hot starch solution to produce a dispersion of fatty acid in the solution.

Fatty acid mixture A A mixture comprising stearic acid (Emersol 120, a commercial stearic acid product containing about 52% palmitic acid and 48% stearic acid with some residual oleic acid), and polyethylene glycol (400) monostearate. Percentages are based on 100% active total solids. The polyethylene glycol monostearate was prepared by ethoxylationof stearic acid with 382 grams of ethylene oxide, which corresponds to about 9 mols of ethylene oxide to 1 mol of stearic acid. (The (400) indicated in the identification of the polyethylene glycol monostearate refers to the molecular weight of the glycol, as determined by the number of mols of ethylene oxide used in its preparation.)

Fatty acid mixture B A mixture of 75% of the commercial stearic acid product above identified, 15% of the above-identified polyethylene glycol (400) monostearate, and 10% polyethylene glycol (400) distearate.

Both of the above mixtures are hard solids at room temperature (75 F.) and after their blending together or premixing (stearic and palmitic acids have melting points of about 86 F. and 148 F., respectively), and are easily flaked to produce a flaked or particulate form facilitating ready mixing of the material with a coating composition. The blended materials while having a melting point well above room temperature, melt readily in hot starch at its usual storage temperature, which is usually above 150 F., normally about 170 F.

A coating composition was prepared from the aboveidentified mixture A, by adding a weight equal to about 3%% of the weight of the starch (.525 part) to the starch solution described, with the solution at a holding temperature of about 170 F. Complete mixing and dispersion of the product in the starch solution occurred almost immediately. The starch solution was then mixed with the aqueous suspension of clay, and a small amount of a biocide added (optional), to prevent spoilage, and a coating composition resulted having a temperature within the range of 100 F. to 110 F. suitable for application to a paper web. A similar coating composition was prepared, only replacing mixture A with mixture B containing the distearate. The coating compositions had a pH within the range of about 5.9 to 6.6.

Coating compositions made in this manner were utilized in the coating of publication grade paper, containing about 50% sulphite bleached pulp and 50% ground wood. Spreads of 4 to 6 pounds per side were used. The coatings spread easily, and there was no evidence of separation of the fatty acid, either in the mixing apparatus where the coating was prepared, or in the paper-making equipment, including the blade used to apply the coating. Supercalendering of the papers was performed, without dusting occurring.

The amount of fatty acid additive mixture used may be varied, with this resulting in a difference in the lubricity of the coatings in the papers finally resulting. Satisfactory papers were produced using as little as 2.5% to as much as 6% of the weight of the starch.

The above-indicated proportions of mineral pigment and binder or adhesive, and the particular materials used as these constituents, of course, is subject to some variation, depending upon the ultimate type and grade of paper desired. Exemplary of other pigments that may be utilized, in addition to the clay, chalk, and titanium oxide already discussed, are calcium sulphate, satin white, and calcium carbonate. In many papers it is common to have or more of such other pigments in the coating, economic factors and physical properties desired in the ultimate type of paper being controlled. In making other grades of paper, such as offset grades were water resistance is desired, protein or casein may be substituted for the starch as the adhesive. In certain grades of paper, latex may be included as an additional ingredient, with from one to five parts of this constituent commonly being added to the coating mixture. Adhesive amounts are variable, with usual paper coating compositions containing from about 8% up to about or of the weight of the mineral pigment. The fatty acid mixtures contemplated have proved workable with all these common forms of paper coating formulations,

The use of a nonionic dispersant is important in obtaining optimum results according to this invention. A fatty acid, such as the palmitic and stearic acid mixture that is present in commercial stearic acid, is insoluble in water. If such stearic acid is incorporated in the coating composition without the dispersant contemplated, mixing in of the acid with, for instance, the starch solution proceeds only with difficulty. With a starch solution at room temperature, a substantial portion of the acid will stay on top of the mixture without blending in, and when agitation is stopped, a crystalline surface appears. Mixing is promoted by heating the starch to above the melting point of the stearic acid, but on cooling of the starch, separation of the acid tends to occur, and if the coating composition is screened as it frequently is before application, the separated stearic acid is removed by the screen. Further, during the processing of the paper, stearic acid may collect, for instance, on the applicator roll of the coating machine, which frequently is surfaced with rubber, and deposits build up on this roll so that uneven coatings result.

The proportion of dispersant to fatty acid employed in the additive mixture contemplated will vary. As little as 3% to as much as 40% of the additive mixture may comprise dispersant, but a preferred range is 10% to 30%. The amount of dispersant used in each instance is some what dependent upon the operating conditions in each particular case, and whether, with a given concentration, the fatty acid is seen to remain in dispersed form, or to separate out during the coating of the paper.

It is preferred that the dispersant and the fatty acid be added together as this promotes proper dispersing action and seems to minimize apparently the amount of dispersant required. They may be added separately, however. For instance, they may be added at different times to the hot starch solution, with the acid melting in the solution and the dispersant serving to hold the acid in suspension even on cooling of the solution. The addition of the dispersant should be at such time as to prevent separation of the acid before the coating composition has been finally processed on the paper. With the acid and dispersant blended and added together in the form of particles such as flakes, easy handling and mixing of the additive results. If a liquid dispersant is contemplated, it may be incorporated with the acid to give a free-flowing powder, by adding the dispersant to an acid melt, where the blend is spray-chillable, to give a dry, free-flowing powder.

Exemplary of other nonionic dispersants employable with the fatty acid with suitable hydrophilic-lipophilie balance in the dispersant, are suchadditional polyhydric alcohol partial esters as condensates of ethylene oxide with fatty acids, to produce polyoxyethylene mono and diesters having from 3 to 50 mols of ethylene oxide. This would be equivalent to glycols of roughly from under 200 to just over 2000 molecular weight. A triethylene glycol monostearate was tested and gave suitable starch slurry viscosity. Polypropylene glycol esters of hydroxy fatty acids and ethers of dihydric fatty alcohols condensed with ethylene oxide are also employable, and illustrative of such condensate in the condensate of ricinoleyl alcohol or dihydroxy stearyl alcohol with several mols (3-25 of propylene oxide, with ethylene oxide reacted with the condensate to make 50% or more of the total molecular weight, Simple polyhydroxy alcohol esters of fatty acids, such as glycerol esters and sorbitan esters with or without a polyoxyethylene content by condensation with ethylene oxide are also suitable, as well as condensates of the fatty alcohol-ethylene oxide type, for example, polyoxyethylene ethers or ricinoleyl alcohol and other long chain fatty alcohols, saturated or unsaturated.

Further illustrating nonionic dispersants for such fatty acid materials are such fatty acid-alkanol amine condensates as monoisopropanol amine condensate with stearic acid, ethoxylated with 4 mols of ethylene oxide, and monoethanol amine-coconut oil fatty acid condensate with a corresponding amount of ethoxylation. The Ethomids produced by Armour are typical of this category. Also, propylene glycol-ethylene oxide condensates, in which a hydrophobic base is prepared by reacting propylene oxide and propylene glycol, and then is condensed with ethylene oxide to provide hydrophilic ends on the chain of the molecule are suitable. These substances are marketed under the name Pluronics by Wyandotte Chemicals.

Paper coating compositions have been prepared using other processes than adding the stearic acid and dispersant mixture to the hot starch solution. For instance, in the so-called Vanderbilt process, a preconverted starch, pigment, and water are all added together and heated to 200 F. for about 20 minutes, with mixing. Proportions of pigment, starch, and water used in this mix may be as indicated in the paper coating composition earlier described. The stearic acid and nonionic dispersant mixture may be added together with the pigment and starch, and during the process of heating and mixing, the fatty acid becomes completely dispersed in the coating composition, to remain so during use of the composition.

In certain other procedures, it may be desirable to prepare a coating composition as first indicated, where a starch solution is precooked, and after this is mixed with an aqueous pigment suspension, and to add the acid and dispersant in the form of a hot water solution, with the hot water solution, starch solution, and pigment suspension all added together at one time and then mixed.

With the coating compositions of the invention, quite surprisingly, less quantities of the stearic acid-dispersant mixture are required to obtain the flowability, and the lubricity desired in finished coated papers, than when conventional materials are used. By way of explanation, it has been found that in a typical production run of coated paper, and using calcium stearate to produce the lubricity desired, some .75 part of stearate is required for every 15 parts starch, in other words, the stearate on a Weight basis represents 5% of the weight of the starch. Using fatty acid and a dispersant as described herein, in an amount equal to 5% of the starch, papers were produced which when tested for a coeflicient of friction showed a slipperiness which was about 15% greater than that of paper using calcium stearate. The amount of acid and dispersant used could be reduced to some 3% of the starch, coated papers resulting having a slipperiness which was substantially the same as that produced with the larger quantities of calcium stearate. Such papers also show the same ability to withstand supercalendering without dustmg.

With the fatty acid and dispersant of the invention, there is no sharp increase in viscosity in the coating composition such as results from materials such as ammonium stearate. A higher solids content, therefore, is possible in mixtures, and there is no restriction placed on the paper maker to the use of a blade-type coater.

While there has been described several modifications of the invention, certain variations and changes will suggest themselves to those skilled in the art. It is desired to cover all modifications and variations as would be apparcut to one skilled in the art, and that come within the scope of the appended claims.

It is claimed and desired to be secured by Letters Patent:

1. For an aqueous coating composition, an additive mixture dispersible in the composition for increasing the lubricity thereof which consists essentially of a liquidvehicle free blend of a fatty acid selected from the group consisting of stearic acid, palmitic acid and mixtures thereof, and a nonionic dispersant for the fatty acid in the form of a polyethylene glycol stearate with a molecular weight of about 400 for the glycolic portion of the stearate, the latter being present in an amount ranging 6 from about 3 to 40% by weight of the fatty acid and in suflicient quantity to disperse the normally water insoluble fatty acid in the aqueous composition, said blend being a solid at room temperature, of suflicient hardness to reduce to particle form, and having a melting point below the boiling point of water.

2. In the manufacture of a paper coating composition from an aqueous mixture including a mineral pigment, and a binder selected from the group consisting of protein, starch, and mixtures thereof the method of adding lubricity to the coating composition comprising preparing a nonemulsified blend of an unsubstituted predominantly hydrogen-saturated fatty acid and a nonionic dispersant for the acid having a chain length of from 14 to 22 carbon atoms which blend functions as an oleaginous material in the coating composition, said blend of fatty acid and dispersant being a hard solid at room temperature, reducing said blend while in solid form to a particulate state to promote the mixing thereof, preparing the aqueous mixture for the reception of said blend by heating the mixture to a temperature above the melting point of the blend, and with said temperature maintained adding said blend to the aqueous mixture, in an amount ranging from about 2.5 to 6% by weight of the binder in the mixture, with the blend on addition melting and becoming mixed thoroughly in the aqueous mixture, an emulsion of the fatty acid in the aqueous mixture forming with mixing of the blend and the dispersant being in sufficient quantity to maintain the fatty acid dispersed in such emulsion.

3. A method of preparing a paper coating composition from a pigment, water, and an adhesive in an amount ranging from about 8 to 30% by weight of the pigment in the coating composition, said adhesive being selected from the group consisting of protein, starch, and mixtures thereof, said method comprising utilizing an unsubstituted essentially hydrogen-saturated fatty acid having a chain length of from 14 to 22 carbon atoms as an oleaginous material for the coating composition; preparing a slurry of the adhesive and water, and cooking the slurry at an elevated temperature which is above the melting point of said fatty acid; with the temperature of said slurry at an elevated temperature, mixing said fatty acid with the slurry, in an amount ranging from 2.5 to 6% by weight of the adhesive in the mixture, with said acid then melting in the slurry; mixing with the slurry while the same is at an elevated temperature a nonionic dispersant for the fatty acid in sufiicient quantity to maintain dispension of the fatty acid in the slurry; preparing an aqueous suspension of the pigment; mixing the aqueous suspension of pigment and said slurry containing the fatty acid and said dispersant; and cooling the product to obtain the coating composition.

4. The method of claim 3, wherein the fatty acid and nonionic dispersant are mixed with said slurry by adding them concurrently to the slurry.

5. In the manufacture of a paper coating composition from water, parts pigment and 8 to 30 parts adhesive, said adhesive being selected from the group consisting of protein, starch, casein and mixtures thereof, the method of adding lubricity to the coating composition through the steps of preparing a slurry of the water and at least the adhesive, cooking such slurry at an elevated temperature, after cooking of the slurry and with the slurry at an elevated temperature adding to the slurry from 1.75 to 5.4 parts of an unsubstituted predominantly hydrogensaturated fatty acid having a chain length of from 14 to 22 carbon atoms which fatty acid functions as an oleaginous material in the coating composition, and a nonionic dispersant for the acid, the fatty acid and dispersant when added being in nonemulsified form, and mixing said fatty acid in the slurry and forming an emulsion of the fatty acid and slurry, the nonionic dispersant which was added being in suificient amount to maintain the fatty acid dispersed in such emulsion.

"7 6. The manufacture of claim 2, wherein the fatty acid is selected from the group consisting of stearic acid, palmitic acid and mixtures thereof, and the nonionic dispersant for the acid comprises a polyethylene glycol stearate with a molecular weight of approximately 400 for the glycolic portion of the stearate.

References Cited UNITED STATES PATENTS 2,621,133' 12/1952 K. M. Garver e181. 106210 2,993,872 7/1961 R. K. Gagnon et al. 106-211 3,020,176 2/1962 Robinson et a1. 117-156 FOREIGN PATENTS 5 1,110,149 7/1961 Germany.

ALEXANDER H. BRODMERKEL, Primary Examiner.

DONALD J. ARNOLD, Examiner.

10 T. MORRIS, Assistant Examiner. 

2. IN THE MANUFACTURE OF A PAPER COATING COMPOSITION FROM AN AQUEOUS MIXTURE INCLUDING A MINERAL PIGMENT, AND A BINDER SELECTED FROM THE GROUP CONSISTING OF PROTEIN, STARCH, AND MIXTURES THEREOF THE METHOD OF ADDING LUBRICITY TO THE COATING COMPOSITION COMPRISING PREPARING A NONEMULSIFIED BLEND OF AN UNSUBSTITUTED PREDOMINANTLY HYDROGEN-SATURATED FATTY ACID AND A NONIONIC DISPERSANT FOR THE ACID HAVING A CHAIN LENGTH OF FROM 14 TO 22 CARBON ATOMS WHICH BLEND FUNCTIONS AS AN OLEAGINOUS MATERIAL IN THE COATING COMPOSITION, SAID BLEND OF FATTY ACID AND DISPERSANT BEING A HARD SOLID AT ROOM TEMPERATURE, REDUCING SAID BLEND WHILE IN SOLID FORM TO A PARTICULATE STATE TO PROMOTE THE MIXING THEREOF, PREPARING THE AQUEOUS MIXTURE FOR THE RECEPTION OF SAID BLEND BY HEATING THE MIXTURE TO A TEMPERATURE ABOVE THE MELTING POINT OF THE BLEND, AND WITH SAID TEMPERATURE MAINTAINED ADDING SAID BLEND TO THE AQUEOUS MIXTURE, IN AN AMOUNT RANGING FROM ABOUT 2.5 TO 6% BY WEIGHT OF THE BINDER IN THE MIXTURE, WITH THE BLEND ON ADDITION MELTING AND BECOMING MIXED THOROUGHLY IN THE AQUEOUS MIXTURE, AN EMULSION OF THE FATTY ACID IN THE AQUEOUS MIXTURE FORMING WITH MIXING OF THE BLEND AND THE DISPERSANT BEING IN SUFFICIENT QUANTITY TO MAINTAIN THE FATTY ACID DISPERSED IN SUCH EMULSION. 